In general, a construction machine such an a hydraulic excavator and so forth to be driven by an hydraulic system is provided with a hydraulic pump which makes maximum load work possible, and a large-sized engine which drives this hydraulic pump so as to cope with all kinds of work from light load work to heavy load work. In particular, in the hydraulic excavator, the maximum load is generated when the work such as excavation, loading and so forth of sediment is performed.
The heavy load work on which such a maximum load is imposed is part of the overall work and the capacity of the engine is left over at the time of the light load work such as horizontal tow and so forth for levelling the ground. This is one of factors which make a reduction in fuel consumption amount (hereinafter, abbreviated as fuel efficiency as the case may be) of the hydraulic excavator difficult. In view of this point, there is known the hybrid construction machine that the engine is miniaturized in order to reduce the fuel efficiency and an output shortage in association with miniaturization of the engine is supported (assisted) with an output by a prime mover and an electrical storage device on which secondary batteries, capacitors and so forth (hereinafter, referred to as batteries) are loaded is used as a power source of the prime mover.
Electric equipment such as the electrical storage device, the prime mover and so forth which configure this hybrid construction machine requires appropriate temperature control for thermal protection and a highly efficient operation of a drive circuit. In particular, in the electrical storage device, when the battery is at an excessively low temperature, internal resistance of the battery is increased, input/output characteristics are remarkably lowered and a reduction in operating capability of the construction machine is brought about. On the other hand, when the battery is at an excessively high temperature, since such deterioration of the battery that the battery capacity is irreversibly lowered or the internal resistance is increased and so forth is promoted, the useful life of the electrical storage device is shortened. Accordingly, it is required for the electrical storage device to be provided with battery cooling and warming-up functions according to the situation.
Conventionally, as the battery cooling and warming-up functions of the electrical storage device, a method of forcibly applying outdoor air (air) which is a heating medium to a battery surface by a fan, a blower and so forth, a method of forcibly introducing a liquid (a coolant) which is the heating element to the battery surface by a pump and so forth and so forth are used. The former method is an air-cooled type and the later method is called a water-cooled type or liquid-cooled type and so forth. In the application to the hybrid construction machine, since it is necessary to protect the heating medium and a passage thereof against dust and many contrivances and improvements are needed when the air-cooled type in which the passage of the heating medium is made as an open system is adopted, the liquid-cooled type in which the passage of the heating medium is made as a closed system is often adopted.
As one of conventional technologies for such a liquid-cooled type electrical storage device, there is known an electrical storage device that a battery block an outer casing can of which is made of a metal and which is made by laminating a plurality of battery cells is fixed onto a cooling plate in which the passage through which a refrigerant is circulated has been formed via a heat transfer member, the battery block and the cooling plate are thermally coupled together and thereby the respective battery cells in the battery block can be cooled in a uniform state (see, for example, Patent Literature 1).
On the other hand, in a case where the conventional electrical storage device disclosed in this Patent Literature 1 has been applied to the hybrid construction machine as it is, since it is feared that each battery cell in the battery block may be directly exposed to the outdoor air, dust, moisture and so forth in a work atmosphere of the hybrid construction machine may be adhered to the battery block of the electrical storage device and thereby a normal operation of the battery and the reliability thereof may be hindered, it is necessary to protect the electrical storage device against these dust, moisture and so forth.
Accordingly, there is proposed a hybrid hydraulic excavator which includes a plurality of capacitor cells for each containing a plurality of capacitors, a cooling plate for cooling each capacitor cell, a top cover for covering the plurality of capacitor cells in a lump and a bottom cover for covering a region where the capacitor cells are attached on the bottom side of the cooling plate, in which the cooling plate has a cover attachment hole which is bored in a thickness direction and into which a screw member for attaching these top cover and bottom cover is inserted, the top cover and the bottom cover which have been fixed to the cooling plate with this screw member cover the capacitor cells and thereby a drip-proof effect and a dust-proof effect for the capacitors can be obtained (see, for example, Patent Literature 2).